The presence of patent ductus arteriosus (PDA) in the small preterm infant is a common and often serious problem. Surgical ligation of the ductus has been the traditional approach to infants unresponsive to usual medical therapy. Recently indomethacin, orally administered, has been proposed as a potentially useful pharmacologic agent for inducing ductal closure in these infants. Early investigations of this technique have yielded conflicting results both as to efficacy and safety of indomethacin when compared with usual medical therapy and surgery. Since no single institution in the United States has enough small preterm infants to evaluate adquately, within a short period of time, the proper role of indomethacin in this condition, a collaborative study among 12 institutions is proposed. An estimated 2000 infants with birth weights of less than or equal to 1750 grams, admitted to these institutions within the first 24 hours of life, will be studied. The first question we propose to answer, via a blinded randomized trial, is whether early administration of indomethacin to infants who develop a PDA will prevent the development of severe congestive failure with prolonged respirator if available, will be used. For infants who do not receive indomethacin in this early trial and whose cardiorespiratory distress does not respond to usual medical therapy, we propose a second randomized trial to test the relative efficacy, and safety, of indomethacin and surgery. The outcome variables to be studied include hospital mortality, duration of ventilatory support, length of hospitalization, and incidence of complications (necrotizing enterocolitis, apnea/bradycardia, etc.). A follow-up evaluation at one year of age of all survivors who had PDA and a subset of infants without PDA will be carried out to elucidate the effects of PDA and its management on the cardiovascular, pulmonary, neurologic, renal, and general developmental status of these babies. Finally by utilizing data from the entire cohort, we will be able to evaluate a variety of perinatal factors as determinants of the occurrence of PDA.